#3: Use a wax that doesn’t stain trim.
#4: I’m not sure what type of buffer they’re referring to, but you should probably just skip it outright. Apply wax with a microfiber applicator instead.
#5: Polishing is probably the trickiest and most time consuming part. I wouldn’t bother learning this until you’ve mastered the other steps.
#6: Break the clay bar into multiple small chunks. Fold the contaminants into the clay frequently. If you drop the clay, throw it away.
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I’ll add my own:
1) Of all detailing steps, washing makes the biggest difference in a cars appearance.
2) Of all detailing steps, washing probably causes the most damage to your paint. Hence the two bucket method.
3) You don’t need to apply a ton of wax. If it’s opaque instead of translucent, you probably applied too much.
4) Wash and detail your wheel wells. Get up in there with a brush and coat with some cheap shine spray. You’ll be amazed at what a difference this will make.

With regard to the #3 tip of your own, I used to work in a detail shop and we’d stretch our wax (liquid or paste) by keeping the applicator damp. It helps to thin the product on the car, which makes stock last longer and doesn’t deliver a compromised result.

You’re really only getting a benefit from the wax that actually makes contact with the paint – no sense in putting it on thick because you’ll end up wiping most of it off again. A thinner layer also makes it easier to “wax off.”